Understanding the structure and properties of geological formations can reduce the cost of drilling wells for oil and gas exploration. Measurements made in a borehole (i.e., down hole measurements) are typically performed to attain this understanding, to identify the composition and distribution of material that surrounds the measurement device down hole. To obtain such measurements, magnetometers are sometimes applied to provide telemetry, ranging, and bit location functions.
Magnetometers with increased sensitivity have recently become available. For example, some references for Rb atomic vapor magnetometers quote sensitivities on the order of 10 fT/Hz5. These units may be able to provide greater telemetry bandwidth, and more precise location, than magnetometers currently in use down hole. However, to operate these units within the Earth's magnetic field, in applications where a bandwidth of 30 Hz or more is desired, a resolution on the order of 27 bits may be needed. If electronic devices with a voltage range of ±12 VDC are used to process these signals, then the desired resolution is equivalent to roughly 90 nanovolts. For this reason, it is extremely difficult to manufacture processing electronics with a noise floor that permits useful operation of these sensors under down hole conditions.